Production of diolefins from olefins



Patented June 9, 1953 PRODUCTION OF DIOLEFINS FROM OLEFINS Charles R.Noddings, George W. Waldron and John W. Corey, Midland, Mich, assignorsto The Dow Chemical Company, Midland, Mich., a corporation of DelawareNo Drawing. Application December 26, 1950; Serial N0. 202,808

4 Claims.

This invention concerns an improved method for the catalyticdehydrogenation of olefines, having at least four carbon atoms in theunsaturated carbon chain of the molecule, to form correspondingaliphatic conjugated diolefines. It pertains more particularly toimprovements in a process wherein such dehydrogenation of an olefine iscarried out at high temperatures in the presence of steam using acatalyst comprising a calcium nickel phosphate as its active principalingredient.

In U. S. Patent No. 2,442,319 it is disclosed that certain normalcalcium nickel ortho-phosphates, and mixtures of the same with minoramounts, e. g. '30 per cent by weight or less, of chromium oxide, arehighly efiective in catalyzing the dehydrogenation of olefines, havingat least four carbon atoms in the unsaturated chain of the molecule inthe presence of steam at reaction temperatures not exceeding 750 C., butthat such catalyst has little, if any, efiect' in catalyzing thedehydrogenation of paraffinic hydrocarbons, or of other olefines, undersuch reaction conditions. Because of its efiectiveness and its selectiveaction in catalyzing the dehydrogenation of olefines having four or morecarbon atoms in the unthe mixture in a neutral to alkaline condition.The precipitate is washed with water, until substantially free ofwater-soluble salts, and dried. It is usually pelletized as such or inadmixture with 30 per cent by weight or less of chr'omic oxide, so as tobring it to a form convenient for use as a catalyst.

U. S. Patents 2,442,320, 2,456,367 and 2,456,368 and a pendingapplication of S. B; Heath, Serial No. 686,134, filed July 25, 1946, nowU. S. Patent No. 2,542,813, issued February 20, 1951, disclosemodifications in the above-described methods of preparing and employingsuch calcium nickel phosphate-containing catalysts.

During attempts to employ the above-discussed normal calcium nickelphosphate-containing catalysts for the production'of aliphaticconjugated diolefines on-a commercial scale using a reaction vessel of akind conventionally employed for such dehydrogenations with othercatalysts,

, unexpected difficulties were encountered. By-

saturated chain of the molecule, such catalyst is suitable for theproduction of an aliphatic conjugated diolefine, e. g. butadiene orisoprene, etc., in high yield and readily purifiable form from eitherpure or impure olefi'nic starting materials. For instance, it may beapplied in producing 1,3-butadiene in good yield and purifiable formfrom l-butylene, 2-but'yl'ene, or a mixture thereof, which contains asubstantial amount or" other hydrocarbons 'such as ethane, propanebutane, pentane, ethylene, propylene, or isobutylene, etc. The catalystpromotes dehydrogenation of the l-butylene and 2-butylene to form1,3-butadiene, but does not catalyze to an appreciable extentdecomposition of the other hydrocarbons. Periodically, the catalyst isfreed of cumulated carbonaceous deposits by treatment at400 C. or abovewith a mixture of steam and air or oxygen.

The catalytically active calcium nickel phosphate contains from 6 to 12,preferably from 7.5 to 9.2, atoms of calcium per atom of nickel, thecalcium. and nickel being chemically combined with ortho-phosphateradicals. It may be formed and precipitated by admixing, in an aqueousmedium, a water-soluble ortho+phosphate, e. g. phosphoric acid or anammonium phosphate, with nitrates or other water-soluble salts ofcalcium and nickel in the proportions theoretically required to formsuch product, while maintaining were caused by a catalytic coactionbetween the calcium nickel phosphate and thewallsof the reaction vesselcontaining the same, which catalytic coaction was widely different fromthe catalytic action of the calcium nickel phosphate alone and was suchas to modify and impair the catalyt ic action of the calcium nickelphosphate contained in the vessel. In other words, materials previouslyrecommended, and employed satisfactorily, for construction of reactorsfor the production of diolefines from olefines with other kinds ofdehydrogenation catalysts are unsatisfactory when using the calciumnickel phosphate containing catalyst.

Ordinary iron and steel cannot satisfactorily be used for constructionof the catalyst chamber.

since they weaken, and are badly corroded at the reaction temperaturesby the steam and air employed in the process. Nickel-bearing alloysteels are adequately strong and resistant-to the action of steam andair at the reaction temperature and have heretofore been usedsatisfactorily in the construction of reactors for the dehydrogenationof olefines to form diolefines in the presence of other dehydrogenationcatalysts. However, a reaction vessel constructed of a nickel-alloysteel is unsatisiactory when employing the calcium nickelphosphate-containing catalyst, since use of such catalyst in contactwith a nickel alloy steel results in extensive by-product formation andin formation or" hard carbonaceous deposits Within the catalyst bodyduring use for the dehydrogenation of an olefine.

To be satisfactory for the construction, or internal lining, of areaction vessel in which the calcium nickel phosphate is to be employedfor the catalytic dehydrogenation of an olefine in the presence of steamto form a corresponding conjugated diolefine, it is necessay that amaterial of construction be rigid and resistant to the action of steamand air at temperatures of from 600 to 750 0.; that it have noappreciable action in catalyzing the decomposition of alivphatichydrocarbons at such temperatures, and

that it be inert to, and have no appreciable efiect' of modifying thecatalytic, action of, the calcium nickel phosphate at such reactiontemperatures.

It is an object of the invention to provide materials which maysatisfactorily be used for the construction, or lining, of reactorswithin which the calcium nickel phosphate-containing-catalyst is to beemployed for the dehydrogenation of olefines in the presence of steam toform corresponding aliphatic conjugated diolefines. An,-

oth'er object is to provide an improved process for the production ofaliphatic conjugated diolefines which comprises passage of a mixture ofa corresponding olefine and steam through a bed of such catalystsupported by, or confined in a chamber having walls of, one or more ofthe materials hereinafter specified. Further objects will be evidentfrom the following description or" the invention.

We have found that a chrome alloy steel, consisting essentially of ironand from 4 to 30 per cent by weight of chromium, and also ceramicmaterials having softening points higher than 750 C. are resistant toattack by air and are substantially inert to steam and aliphatichydrocarbons at temperatures in the order of from 550 to 750 C.; aresufficiently strong and rigid for support and confinement of the calciumnickel phosphate-containing catalyst at such tempera- .tures; and haveno appreciable effect at such ;temperatures of catalyzing decompositionor car- .bonization of the hydrocarbons in the reaction mixture, or ofmodifying appreciably the catalytic action of the calcium nickelphosphate catalyst in contact therewith. Accordingly, the full catalyticeffect, selectivity, and active life of the calcium nickelphosphate-containing catalyst in catalyzing the dehydrogenation ofolefines in the presence of steam to form corresponding conjugateddiolefines may be obtained, provided the catalyst is supported on, andretained or confined by, one or more of the above-named structuralmaterials during employment in the reaction.

It is important that the structural material be substantially free ofnickel, since nickel, if present in the inner walls of the reactor,coacts catalytically with the calcium nickel phosphate catalyst to causeconsiderable by-product formation, e. g. carbonization and cracking ofcarbon chains of the hydrocarbons fed to the dehydrogenation, and theresultant formation of by-products such as carbon, tarry material,methane,

' of ceramic material.

ethane, propane, ethylene, propylene, or acetylenic hydrocarbons, etc.,becomes more extensive as the dehydrogenation reaction is continued. Anyof the usual chrome alloy steels which are substantially free of nickel,e. g. alloy steel containing from 96 to 69.5 per cent of iron and from 4to 30 per cent of chromium, together usually with 0.5 per cent byweightor less of carbon, may be employed for support of the catalystduring employment in the dehydrogenation process. The ceramic materialsare, of course, usually free from nickel. Examples of ceramic materialssuitable for use in contact with the calcium nickel phosphate catalystare quartz or silica which has been fused and formed into tubes, tile,rods, or other shapes having extended surfaces, alumina, aluminumsilicate, and brick, tile, or tubes of baked clay. All such ceramicmaterials have softening points above 750 C. and have propertiesrendering them suitable for retention, or confining, of a bed of thecalcium nickel phosphate catalyst during employment of the latter forthe dehydrogenation of an olefine to form a corresponding aliphaticconjugated diolefine.

The reaction chamber in which the catalyst is employed may be of anyusual design, e. g. it may consist merely of a tower or chamber forholding a bed of the catalyst and provided with an inlet and outlet forpassage of the reaction vapors through the bed. A number of reactionchambers of suitable design are known. The reaction chamber may beconstructed of, or lined internally with, a chrome alloy steel which isfree of nickel, or it may be constructed of ordinary structural steel,e. g. a carbon steel, and be lined on the inside with brick, tile,tubing, or a cement, I'he requirement that the reactor be constructedof, or lined internally with, one or more of the structural materialsjust mentioned pertains only to the portions of the reactor which are indirect contact with the calcium nickel phosphate catalyst duringemployment of the latter in the process, e. g. other internal surfacesof the reactor may be constructed of any suitable structural materialsincluding, if desired, a nickel alloy steel or a nickel-chromium alloysteel. However, during practice of the process, there is chance thatparticles of the catalyst may be blown into contact with internalsurfaces of the reactor other than those supporting the catalyst bed,hence all internal Walls of the reactor are usually, and advantageouslyconstructed of a chromium alloy steel or a ceramic material.

Except for the requirement that the calcium nickel phosphate catalystbed be supported or retained by surfaces of a chrome-alloy steel or aceramic material, the process for production of an aliphatic conjugateddiolefine is similar to that described in U. S. Patent No. 2,442,319.The reaction chamber is charged with the granular calcium nickelphosphate-containing catalyst which may include a minor amount of alubricant, such as graphite, vegetable oil, or a hydrocarbon oil, etc.,used as a binder in forming pellets of the catalyst. Such lubricant, ifpresent, is removed by passing air, or preferably a mixture of aboutequal volumes of air and steam, through the catalyst bed at temperaturesbetween 450 and 750 C. When such lubricant is'a material capable ofbeing vaporized, e. g. a mineral or vegetable oil, the step of treatingthe catalyst withair be preceded by one of passing an inert gas such assteam, nitrogen, or carbon dioxide over the catalyst so as to vaporizeand remove at least a P011 101 of the binder from the catalyst granules.

In instances, in which the catalyst is obtained in a form free oflubricant; or other organic impurities, the preliminary treating stepsvjust described may be omitted.

When substantially free of carbon-containin impurities, the catalyst bedis swept free of air with steam and is heated to the desired reactiontemperature preferably by passing superheated steam through the reactionchamber containing the catalyst. A mixture of steam and the olefinereactant, e. g. butylene, amylene, or a hexylene, or a mixture of steamand such olefine together with other parafiinichydrocarbons or witholefinic hydrocarbons having the same or a lesser number of carbon atomsin the molecule as that possessed by the olefinic reactant, is passedthrough the reaction chamber and the catalyst bed therein, at reactiontemperatures not exceeding 750 C., e. g. between 550 and 750 C. andpreferably between 600 and 700 C. The usual procedure is to pass theolefine-containing gas into admixture with steam which has beensuperheated to 750 C. or above, i. e. to a temperature suilicient sothat the resultant mixture is at the desired reaction temperature, andto pass the mixture through the reaction vessel containing the calciumnickel phosphate catalyst. If desired, the heat may be supplied in otherways, such as by forming the steam and hydrocarbon mixture at a lowertemperature and passing the mixture through a preheater to bring it tothe desired temperature. The yield of diolefine is usually highest whenfrom 15 to 20 volumes of steam are employed per volume of the reactiveolefine in the hydrocarbon starting material, but the steam may be usedin larger proportions if desired. The rate of vapor flow through thecatalyst chamber may be varied widely, but usually corresponds tobetween 50 and 700 liters of the olefine (expressed as at 0 C. and 760millimeters absolute pressure)per liter of catalyst bed per hour.

The vapors flowing from the catalyst chamber are ordinarilypassedthrough heat exchangers and other cooling devices to condense andremove the water from the hydrocarbon products. The conjugated diolefineproduct may be separated from the other hydrocarbons in usual ways, e.g. by reaction with sulphur dioxide or cuprous ammonium salts to form adouble compound, and the unreacted olefine be recycled in the process.

By operating as just described using a reaction vessel of, or internallylined with, a chrome alloy steei or a ceramic material for support andretention of the calcium nickel phosphate catalyst,

the olefine, or olefines, in the feed mixture which have four or morecarbon atoms in an unsaturated carbon chain of the molecule areselectively dehydrogenated to form a corresponding conjugated diolefine,or diolefines, in excellent yield and readily purifiablform.Carbonization and other side reactions occur to only a minor extent.However, the catalyst bed does gradually accumulate a small amount ofcarbon,- or nonvolatile organic material, and decreases in catalyticactivity. Accordingly, flow of the hydrocarbon starting material isperiodically interrupted and a mixture of air and steam is passed attemperatures between 450 and 700 C., and preferably at thedehydrogenation temperature, through the reaction chamber and the bed ofcatalyst therein to oxidize and remove the. carbonaceous, or organic,material and thus reactivate the catalyst. From to 30 minutes is,usually required for carrying out such reactivation step. The. reactionchamber is then again swept free of air with catalyst.

. steam, after which the introduction of an olefine together with thesteam is. resumed. Usually, reactivation is advisable after from 30- to60 minutcs of employment of the: catalyst in the dehydrogenation'reaction. In practice, two or more catalyst chambers ar employed in asystem pro-- vided with connections for passing the reaction mixturealternately through different beds of the Onev catalyst chamber isreactivated while another is being employed in the dehydrogenation:reaction. By operating in this way, the dehydrogenation is. carried outin a continuous manner.

The: following xamples describe ways. in which the'inv'ention has. beenpracticed and illustrate certain of its advantages, but are not to beconstrued as limiting the invention.

EXAMPLE 1 In each of twoexperiments, a reaction tube of 1 inch internaldiameter was'filled to a depth of ll inches with pellets of a catalyticmixture of 94.7 percent by weight of a normal calcium nickelortho-phosphate, containing approximately 8 atoms of calcium per atom ofnickel, and 5.3 per cent of chromic oxide. The pellets were each 5 inchthick and of t -inch diameter. The catalyst used'in both experiments wasfrom the same source and was identical. A tube of a nickel chromiumalloy steel, known as KAZS and containing approximately 18-per centbyweight of chromium, 8 per cent of nickel, less than 0.5 per cent ofcarbon, and the remainder iron, was used as the reaction tube in one ofthe experiments. The reaction tube employed in the other experiment wasof a chromium alloy steel known as Alleghany 55, which steel containsapproximately 25 per cent by weight of chromium, less than 0.5 per centor" carbon, and the remainderiron. In each experiment, a mixture of from15"to 20 parts, byvolume of steam and one part of gaseous hydrocarbons,containing from 70 to per cent by weight of normal butylenes, i. e.l-butylene and 2-butylene, from 23 to 8 per cent of butanes, about 4 percent of isobutylene, about 3 per cent of 1,3-butadiene, and, about 1 percent of C5 hydrocarbons. was passed at temperatures of from 600 to 630C. through one of the above-mentioned reaction tubes for 30 minutes. Thefeed of hydrocarbons was then interrupted and carbonaceous accumulationswere oxidized and removed from the catalyst bed by passing a mixture ofair and the steam. through the reaction tube at, temperatures of about600-630 C. for approximately 30 minutes. The flow of air was thendiscontinued, air quickly being blown from the tube by the steam, andthe feed of hydrocarbons together with the steam was resumed. This cycleof operations, which required about one hour, was repeated 2,500 timesin each experiment. It may be mentioned that the hydrocarbon mixturesfed to the reaction were drawn from cylinders and that the relativeproportions of normal butylenes and butanes in the hydrocarb-on feedmaterial varied somewhat when one cylinder became exhausted and wasreplaced by another. It is for this reason that the composition of thehydrocarbon feed material is given above as being within stated limits.The hydrocarbons in each cylinder had been analyzed so that thecomposition of the hydrocarbons fed to the reaction in, each 'cycle ofoperations was known. It may also be mentioned that the material duringthe reaction caused small changes in the conversion, 1. e. in theproportion of the hydrocarbons consumed in a given cycle of operations,but did not cause appreciable change in the per cent yield of1,3-butadiene based on the amount of normal butenes consumed. Forconvenience, such yield of 1,3-butadiene, based on the normal butylenesconsumed, is hereinafter referred to as the per cent selectivity of thereaction. Since the principal purpose of the experiments was todetermine the effect of reaction chamber walls on the selectivity of thecatalytic dehydrogenation reaction and since the changes in compositionof the hydrocarbon feed material upon replacing one cylinder of suchmaterial with another did not have appreciable sheet on the selectivity,it is sufficient to state that the hydrocarbon starting materials wereof compositions within the limits hereinbefore stated and is unnecessaryto give the exact composition of the hydrocarbon starting material atvarious stages in the process. The experiment using the KAZS reactiontube was started using a reaction vapor feed mixture containing 15 partsby volume of steam per part of the hydrocarbons therein. It was formedby passing steam through a preheater wherein it was superheated to atemperature such that, upon mixing the same with a stream of thehydrocarbon vapors, the resultant mixture was at a temperature of 600 C.The

rate of flow of the hydrocarbon stream into admixture with the steam was200 volumes of the gaseous hydrocarbons (expressed as at C. and

760 millimeters absolute pressure) per volume of the catalyst bed perhour. The temperature and rate of flow of the steam was maintainedsubstantially constant throughout the first 1700 cycles or" operation.In the catalyst reactivation step of each of the first 2,130 cycles ofoperation, the rate of air feed into admixture with the steam and thenthrough the reaction tube was 85 volumes of air (expressed as at 0 C.and 760 millimeters absolute pressure) per volume of the catalyst bedper hour. In the dehydrogenation stage of each cycle of operations, thevapors flowing from the reaction tube were cooled sufiiciently tocondense the steam. The remaining gaseous products were collected andanalyzed to determine the amounts of unconsurned normal butylcues and of1,3-butadiene therein. On a basis of these values and the knowncomposition of the hydrocarbon starting mixture, there were calculated,for each 500 cycle period of the process, the per cent of the butylenesin the starting mixture which were consumed in the reaction (which valueis hereinafter referred to as the per cent conversion) and the per centyield of 1,3-butadiene based on the normal butylenes consumed, i. e. theselectivity of the reaction. During operation with the KAZS reactiontube under the conditions stated above, the selectivity remained highfor about 500 cycles of operation, but decreased markedly during thenext 1000 cycles.

' At the end oi 1700 cycles the rate of hydrocarbon feed to the reactionwas increased from 200 to 275 volumes of the same per volume of catalystbed per hour and the reaction temperature was increased from 600 to 630C. in attempt to obtain improved conversionand selectivity values.However, the selectivity continued to decrease. When 2,130 cycles ofoperations had been carried out, the rate of air flow in the catalystreactivation step was increased from 85 to 150 volumes of air (expressedas at 0 C. and 760 millimeters absolute pressure) so as to assuresubstantially complete oxidation of the carbonaceous accumu lations inthe catalyst bed during eachof the subsequent cycles of operation.

The experiment using the Alleghany 55 tube was carried out using ahydrocarbon starting mixture of composition within the limits statedabove and using one hour cycles of operations similar to those employedin the above experiment. leghany 55 reaction tube, there was noappreciable decrease in the reaction selectivity during the 2,500 cyclesof operation, and the activity of the catalyst did not decreaseappreciably until after 2,000 operating cycles. Accordingly, the ratesof flow of the several gaseous starting materials were maintainedconstant throughout the experiment. The rate of hydrocarbon feed was275. volumes of gaseous hydrocarbons (expressed as at 0 C. and 760millimeters absolute pressure) per volume of the catalyst bed per hour.The rate of steam feed was such that the mixture entering the reactionzone contained 15 parts by volume of steam per part of the gaseoushydrocarbons. In the catalyst reactivation step of each operating cycle,the rate of air feed was volumes of air per volume of the catalyst bedper hour. During the first 2,300 cycles of operation, thedehydrogenation reaction was carried out at a temperature of 600 C. Thereaction temperature was then raised to 630 C. and maintained at thatvalue during the remainder of the experiment. The hydrocarbon productsfrom each cy- .cle of operations were collected and analyzed asdescribed above. From the analysis and the known composition of thehydrocarbon starting material, the per cent conversion and per centselectivity values for each successive 500 cycle period of the processwere calculated.

The following table identifies each experiment by stating the kind ofreaction tube employed. It gives the average per cent'conversion andaverage per cent selectivity values for each of the successive 500 cycleperiods of operation in each experiment. 7

Two experiments were carried out in a manner similar to that describedin Example 1, except that the reaction tubes, each of 1 inch internaldiameter, were constructed of KAZS steel and of silica, respectively.The catalyst employed in each experiment was material from a larger bedof catalyst that had been used for 66 days in a vessel of a nickelchromium alloy steel (i. e. a steel containing 18 per cent of chromiumand 8 per cent of nickel) for the dehydrogenation of normal butylenes toform 1,3-butadiene and had been found unsatisfactory during use in suchvessel. Except for having been used, the catalyst was similar to thatemployed in Example 1. The amount of catalyst employed in eachexperiment of this example was the same as in Example 1. Also, thehydrocarbon feed mixtures However, in the experiment using theAlemployed in both experiments were the same and were of a compositionwithin the limits given in Example 1. Throughout the dehydrogenationsteps of each experiment, the rate Or" feed of hydrocarbons to thereaction mixture was 275 volumes of the gaseous hydrocarbons (expressedas at C. and 760 millimeters absolute pressure) per volume of thecatalyst bed per hour and steam was fed at a rate such that the reactionmixture, when formed, contained parts by volume of steam per part of thegaseous hydrocarbons. In the catalyst reactivation steps of eachexperiment, the rate of air feed was 85 volumes of air (expressed as at0 C. and 760 millimeters absolute pressure) per volume of the catalystbed per hour. A dehydrogenation reaction temperature of 620 C. was usedin the first 252 cycles of operation in the experiment employing theKAZS tube, and a reaction temperature of 640 C. was employed during there- L mainder of the experiment. In the experiment carried out with thefused silica tube, the dehydrogenation reaction temperature was 620 C.for the first 480 cycles of operation and thereafter was 650 C. Thereaction selectivity decreased rapidly in the experiment using the KAZStube and the experiment was terminated after 300 cycles of operation.The reaction selectivity increased during the experiment with the fusedsilica tube and the experiment was car- 0 ried out over a period of 500cycles. The hydrocarbon products from the dehydrogenation step in eachoperating cycle of each experiment were analyzed to determine theamounts of unconsumed normal butylenes and of 1,3-butadiene therein.From the analyses and the known composition of the hydrocarbon feedmixture, the average conversion value and the average selectivity valuewere calculated for each of three successive 100 cycle periods ofoperation in each experiment and for the final 200 cycles of operationwith the reaction tube of fused silica. These values for each experimentare given in Table II. The table identifies each experiment by statingthe kind of reaction tube employed.

Other modes of applying the principle of the invention may be employedinstead of those explained, change being made as regards the methodherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed.

We claim:

1. In a method wherein an olefine having at least 4 carbon atoms in theunsaturated carbon chain of the molecule isdehydrogenated to form acorresponding aliphatic conjugated diolefine by passing the olefine,together with steam, at reaction temperatures not exceeding 750 C.through a bed of a dehydrogenation catalyst comprising, as itscatalytically active principal ingredient, a normal calcium nickelortho-phosphate material having, chemically combined with the phosphateradicals, from 6 to 12 atoms of calcium per atom ofnickel, the step ofsup porting the bed of catalyst on, and confining it by, surfaces of atleast one substantially inert solid material, of the group consisting ofnickelfree chromium alloy steels and ceramic materials which are solidand rigid at the reaction temperature, while carrying out the reactionby passing the heated reaction vapors through the catalyst bed and intocontact with the material confining the bed.

2. A method, as described in claim 1, wherein the solid materialconfining, and in contact with, the bed of catalyst is a chromium alloysteel which is free of nickel.-

3. A method, as described in claim 1, wherein the solid materialconfining, and in contact with, the bed of catalyst is a ceramicmaterial which is solid and rigid at the reaction temperature.

4; A method, as described in claim 1, wherein the solid materialconfining, and in contact with, the bed of catalyst is silica.

CHARLES R. NCDDINGS. GEORGE W. WALDRON. JOHN W. COREY.

References Cited in the file of this patent UNITED STATES PATENTS 7Number Name Date 2,265,641 Grosskinsky et a1. Dec. 9, 1941 2,347,527Vanderbilt Apr. 25, 1944 2,442,319 Britton et al May 25, 1948

1. IN A METHOD WHEREIN AN OLEFINE HAVING AT LEAST 4 CARBON ATOMS IN THEUNSATURATED CARBON CHAIN OF THE MOLECULE IS DEHYDROGENATED TO FORM ACORRESPONDING ALIPHATIC CONJUGATED DIOLEFINE BY PASSING THE OLEFINE,TOGETHER WITH STEAM, AT REACTION TEMPERATUES NOT EXCEEDING 750* C.THROUGH A BED OF A DEHYDROGENATION CATALYST COMPRISING, AS ITSCATALYTICALLY ACTIVE PRINCIPAL INGREDIENT, A NORMAL CALCIUM NICKELORTHO-PHOSPHATE MATERIAL HAVING, CHEMICALLY COMBINED WITH THE PHOSPHATERADICALS, FROM 6 TO 12 ATOMS OF CALCIUM PER ATOM OF NICKEL, THE STEP OFSUPPORTING THE BED OF CATALYST ON, AND CONFINING IT BY, SURFACES OF ATLEAST ONE SUBSTANTIALLY INERT SOLID MATERIAL, OF THE GROUP CONSISTING OFNICKELFREE CHROMIUM ALLOY STEELS AND CERAMIC MATERIALS WHICH ARE SOLDAND RIGID AT THE REACTION TEMPERATURE, WHILE CARRYING OUT THE REACTIONBY PASSING THE HEATED REACTION VAPORS THROUGH THE CATALYST BED AND INTOCONTACT WITH THE MATERIAL CONFINING THE BED.